public static byte[] getHash(byte[] data, int offset, int length) {
byte[] tmp = new byte[20];
try {
MessageDigest md = MessageDigest.getInstance("SHA-1");
md.update(data, offset, length);
md.digest(tmp, 0, tmp.length);
} catch (GeneralSecurityException e) {
// algorithm not found - not in this implementation
throw new RuntimeException(
"SHA-1 algorithm for MessageDigest not supported");